Lobe Seperation

[Loadclr]

How do you find out what your lobe seperation is when you cam sheet doesn't give it? I know it has to do with the lobe centers, but beyond that I don't know diddley. Mine has lobe centers of 109 for the intake and 119 for the exhaust. What lobe seperation do I have? Just wondering.

[johnisbubba]

114 Would be my guess

[lafinrat]

Yes that's 114 LSA 5 degrees advanced. Here's a picture that may be worth 1000 words

[Loadclr]

So, I can then presume that the lower the seperation, there is more lope to the idle and more power?

[already7]

Originally Posted by lafinrat

Yes that's 114 LSA 5 degrees advanced. Here's a picture that may be worth 1000 words

1000 words indeed. Nice pic mang!

[lafinrat]

Originally Posted by Loadclr

So, I can then presume that the lower the seperation, there is more lope to the idle and more power?

Tighter (lower numerical) lobe seperation creates more overlap, which will bleed low speed cylinder pressure and make the idle rougher and vacuum lower. The increased overlap can help charge the cylinder while both valves are open creating a quicker spike in the torque curve. Tight lobe centers usually create quick abrupt torque. Wide usually creates more flat even torque. All this is provided the remainder of the combination stays the same.

[Loadclr]

Just out of curiousity, what's the tightest lobe seperation out there? I've heard of 112, but is there tighter?

[johnisbubba]

Ive seen 110 but I havent really been looking.

[lafinrat]

Originally Posted by Loadclr

Just out of curiousity, what's the tightest lobe seperation out there? I've heard of 112, but is there tighter?

Some circle track cams for smaller motors are in the 104 range. Most drag small-blocks are 105-108. Big blocks are 107-110. Most fuel-injection cars with factory computers need 112-116, depending on the duration. Lower duration cams can have tighter centers and still create excellent vacuum. Turbo and blower motors bring forth a whole new set of veriables. Most all turbo/blower cams will be in the 114-120 range to minimize overlap and keep the intake charge from blowing out the exhaust valve.